Lubricant composition

ABSTRACT

Lubricants can be stabilized against oxidation by the addition of a) a sterically hindered amine and b) a phenol of formula I   &lt;IMAGE&gt; I wherein A, is hydrogen, alkyl, cycloalkyl, phenylalkyl, phenyl or alkylthiomethyl, B is alkyl, cycloalkyl, phenylalkyl, phenyl or alkylthiomethyl and X is hydrogen, alkyl or substituted alkyl. It is preferred to use phenols of formula I which contain a thioether group.

This is a continuation of application Ser. No. 07/546,277, filed on Jun. 28, 1990, now abandoned.

The present invention relates to lubricant compositions which are stabilized against oxidative degradation. Stabilization is effected by the incorporation of at least two specific additives.

It is known and conventional to incorporate additives into lubricants based on mineral oils or synthetic oils in order to improve their general use properties. Additives for stabilizing lubricants against oxidative degradation, known as antioxidants, are especially important. The oxidative degradation of lubricants is particularly significant in the case of engine oils, because high temperatures prevail in the combustion chamber of engines and, as well as oxygen, nitrogen oxides (NO_(x)) are present and act as oxidation catalysts.

The antioxidants used for lubricants are, in particular, organic sulfur and phosphorus compounds and also aromatic amines and phenols, especially sterically hindered phenols (see e.g. Ullmanns Encyklopadie der technischen Chemie (Ullmann's Encyclopaedia of Chemical Technology), 4th edition, Verlag Chemie, volume 20 (1981), page 541-43).

Sterically hindered amines have also already been proposed as stabilizers for lubricating oils, e.g. in U.S. Pat. No. 4,069,199 or JP-A-85/28496.

EP-A-356 677 has proposed mixtures of aromatic amines and sterically hindered amines as antioxidants for lubricants, it also being possible for phenolic antioxidants to be added to these mixtures.

It has been found that combinations of phenolic antioxidants with sterically hindered amines are outstandingly suitable for the stabilization of lubricants, even without the addition of aromatic amines.

The present invention relates to a lubricant composition comprising

(A) a mineral or synthetic oil or a mixture of such oils,

(B) at least one sterically hindered amine and

(C) at least one phenol of formula I ##STR2## wherein A is hydrogen, C₁ -C₂₄ alkyl, C₅ -C₁₂ cycloalkyl, C₇ -C₉ phenylalkyl, phenyl or a group --CH₂ --S--R¹ or ##STR3## B is C₁ -C₂₄ alkyl, C₅ -C₁₂ cycloalkyl, C₇ -C₉ phenylalkyl, phenyl or a group --CH₂ --S--R¹, X is hydrogen, C₁ -C₁₈ alkyl or one of the groups --C_(a) H_(2a) --S_(q) --R², --C_(b) H_(2b) --CO--OR³, --C_(b) H_(2b) --CO--N(R⁵)(R⁶), --CH₂ N(R¹⁰)(R¹¹) and ##STR4## R¹ is C₁ -C₁₈ alkyl, phenyl or a group --(CH₂)_(c) --CO--OR⁴ or --CH₂ CH₂ OR⁹, R² is hydrogen, C₁ -C₁₈ alkyl, phenyl, benzyl or a group ##STR5## R³ is C₁ -C₅₀ alkyl or one of the groups ##STR6## wherein Q is C₂ -C₈ alkylene, C₄ -C₆ thiaalkylene or a group --CH₂ CH₂ (OCH₂ CH₂)_(d) --, R⁴ is C₁ -C₂₄ alkyl, R⁵ is hydrogen, C₁ -C₁₈ alkyl or cyclohexyl, R⁶ is C₁ -C₁₈ alkyl, cyclohexyl, phenyl, C₁ -C₁₈ alkyl-substituted phenyl or one of the groups ##STR7## or R⁵ and R⁶ together are C₄ -C₈ alkylene which can be interrupted by --O-- or --NH--, R⁷ is hydrogen, C₁ -C₄ alkyl or phenyl, R⁸ is C₁ -C₁₈ alkyl, R⁹ is hydrogen, C₁ -C₂₄ alkyl, phenyl, C₂ -C₁₈ alkanoyl or benzoyl, R¹⁰ is C₁ -C₁₈ alkyl, cyclohexyl, phenyl, C₁ -C₁₈ alkyl-substituted phenyl or a group ##STR8## R¹¹ is hydrogen, C₁ -C₁₈ alkyl, cyclohexyl or a group ##STR9## or R¹⁰ and R¹¹ together are C₄ -C₈ alkylene which can be interrupted by --O-- or --NH--, a is 0, 1, 2 or 3, b is 0, 1, 2 or 3, c is 1 or 2, d is 1 to 5, f is 2 to 8 and q is 1, 2, 3 or 4, or, as component (C), a mixture of polyphenols formed by reacting at least one phenol of the formula ##STR10## with at least one phenol of the formula ##STR11## and with formaldehyde or paraformaldehyde, wherein C, D and E independently of the others are C₁ -C₂₄ alkyl, cyclohexyl or phenyl, the composition containing no aromatic amine.

In this composition, the weight ratio of (B) to (C) is preferably 1:1 to 1:100, especially 1:3 to 1:20. The sum of (B) and (C) is preferably 0.05 to 5% by weight, especially 0.1 to 3% by weight, of (A).

A and B as C₁ -C₂₄ alkyl can be linear or branched alkyl, e.g. methyl, ethyl, i-propyl, t-butyl, s-butyl, s-pentyl, t-pentyl, n-hexyl, i-hexyl, t-hexyl, i-heptyl, n-octyl, t-octyl, s-decyl, s-dodecyl, n-dodecyl, s-tetradecyl, n-hexadecyl, n-octadecyl, s-octadecyl or n-eicosyl.

A and B as cycloalkyl can be e.g. cyclopentyl, cyclohexyl or cyclooctyl, especially cyclohexyl. A and B as phenylalkyl can be e.g. benzyl, phenylethyl, phenylpropyl or α,α-dimethylbenzyl.

R⁵ and R⁶ alkyl can be e.g. methyl, ethyl, propyl, butyl, pentyl, hexyl, octyl, decyl or dodecyl. R¹, R², R³ and R⁸ as C₁ -C₁₈ alkyl can also be e.g. tetradecyl, hexadecyl or octadecyl. R⁴ as C₁ -C₂₄ alkyl can also be e.g. eicosyl or tetraeicosyl.

The subscript a is preferably 0, 1 or 2, especially 0 or 1; b is preferably 0, 1 or 2, especially 1 or 2; q is preferably 1 or 2, especially 1.

Component (A) is a mineral or synthetic base oil of the kind conventionally used for the preparation of lubricants. Synthetic oils can be e.g. esters of polycarboxylic acids or of polyols, aliphatic polyesters or poly-α-olefins, silicones, phosphoric acid esters or polyalkylene glycols. The lubricant can also be a grease based on an oil and a thickener. Such lubricants are described e.g. in D. Klamann "Schmierstoffe und artverwandte Produkte" ("Lubricants and Generically Related Products"), Verlag Chemie, Weinheim 1982.

Component (B) can be any cyclic or non-cyclic, preferably cyclic, sterically hindered amine. (B) is preferably a compound containing at least one group of formula II ##STR12## wherein R is hydrogen or methyl. R is preferably hydrogen. Said compounds are derivatives of polyalkylpiperidines, especially of 2,2,6,6-tetramethylpiperidine. These compounds preferably carry one or two polar substituents or a polar spiro ring system in the 4-position of the piperidine ring. They can be low-molecular, oligomeric or polymeric compounds.

The following classes of polyalkylpiperidines are of particular importance:

a) Compounds of formula III ##STR13## wherein n is a number from 1 to 4, preferably 1 or 2, R is hydrogen or methyl, R¹¹ is hydrogen, oxyl, hydroxyl, C₁ -C₁₂ alkyl, C₃ -C₈ alkenyl, C₃ -C₈ alkynyl, C₇ -C₁₂ aralkyl, C₁ -C₁₈ alkoxy, C₅ -C₈ cycloalkoxy, C₇ -C₉ phenylalkoxy, C₁ -C₈ alkanoyl, C₃ -C₅ alkenoyl, C₁ -C₁₈ alkanoyloxy, benzyloxy, glycidyl or a group --CH₂ CH(OH)--Z, wherein Z is hydrogen, methyl or phenyl, R¹¹ preferably being H, C₁ -C₄ alkyl, allyl, benzyl, acetyl or acryloyl, and R¹² when n is 1 is hydrogen, C₁ -C₁₈ alkyl which may be interrupted by one or more oxygen atoms, cyanoethyl, benzyl, glycidyl, a monovalent radical of an aliphatic, cycloaliphatic, araliphatic, unsaturated or aromatic carboxylic acid, carbamic acid or phosphorus-containing acid, or a monovalent silyl radical, preferably a radical of an aliphatic carboxylic acid having 2 to 18 C atoms, of a cycloaliphatic carboxylic acid having 7 to 15 C atoms, of an α,β-unsaturated carboxylic acid having 3 to 5 C atoms or of an aromatic carboxylic acid having 7 to 15 C atoms, R¹² when n is 2 is C₁ -C₁₂ alkylene, C₄ -C₁₂ alkenylene, xylylene, a divalent radical of an aliphatic, cycloaliphatic, araliphatic or aromatic dicarboxylic acid, dicarbamic acid or phosphorus-containing acid, or a divalent silyl radical, preferably a radical of an aliphatic dicarboxylic acid having 2 to 36 C atoms, of a cycloaliphatic or aromatic dicarboxylic acid having 8-14 C atoms or of an aliphatic, cycloaliphatic or aromatic dicarbamic acid having 8-14 C atoms, R¹² when n is 3 is a trivalent radical of an aliphatic, cycloaliphatic or aromatic tricarboxylic acid, of an aromatic tricarbamic acid or of a phosphorus-containing acid, or a trivalent silyl radical, and R¹² when n is 4 is a tetravalent radical of an aliphatic, cycloaliphatic or aromatic tetracarboxylic acid.

Any C₁ -C₁₂ alkyl substituents are e.g. methyl, ethyl, n-propyl, n-butyl, sec-butyl, tert-butyl, n-hexyl, n-octyl, 2-ethylhexyl, n-nonyl, n-decyl, n-undecyl or n-dodecyl.

R¹¹ or R¹² as C₁ -C₁₈ alkyl can be e.g. the groups listed above and additionally n-tridecyl, n-tetradecyl, n-hexadecyl or n-octadecyl, for example.

R¹¹ as C₃ -C₈ alkenyl can be e.g. prop-1-enyl, allyl, methallyl, but-2-enyl, pent-2-enyl, hex-2-enyl, oct-2-enyl or 4-tert-butylbut-2-enyl.

R¹¹ as C₃ -C₈ alkynyl is preferably propargyl.

R¹¹ as C₇ -C₁₂ aralkyl is especially phenethyl and in particular benzyl.

R¹¹ as C₁ -C₈ alkanoyl is, for example, formyl, propionyl, butyryl or octanoyl, but preferably acetyl, and R¹¹ as C₃ -C₅ alkenoyl is especially acryloyl.

R¹² as a monovalent radical of a carboxylic acid is, for example, an acetic acid, caproic acid, stearic acid, acrylic acid, methacrylic acid, benzoic acid or β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid radical.

R¹² as a divalent radical of a dicarboxylic acid is, for example, a malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, maleic acid, itaconic acid, phthalic acid, dibutylmalonic acid, dibenzylmalonic acid, butyl(3,5-di-tert-butyl-4-hydroxybenzyl)malonic acid or bicycloheptenedicarboxylic acid radical.

R¹² as a trivalent radical of a tricarboxylic acid is e.g. a trimellitic acid, citric acid or nitrilotriacetic acid radical.

R¹² as a tetravalent radical of a tetracarboxylic acid is e.g. the tetravalent radical of butane-1,2,3,4-tetracarboxylic acid or of pyromellitic acid.

R¹² as a divalent radical of a dicarbamic acid is, for example, a hexamethylenedicarbamic acid or 2,4-toluylenedicarbamic acid radical.

Preferred compounds of formula III are those in which R is hydrogen, R¹¹ is hydrogen or methyl, n is 1 and R¹² is C₁ -C₁₈ alkyl or n is 2 and R¹² is the diacyl radical of an aliphatic dicarboxylic acid having 4-12 C atoms.

The following compounds are examples of polyalkylpiperidine compounds of this class:

1) 4-hydroxy-2,2,6,6-tetramethylpiperidine

2) 1-allyl-4-hydroxy-2,2,6,6-tetramethylpiperidine

3) 1-benzyl-4-hydroxy-2,2,6,6-tetramethylpiperidine

4) 1-(4-tert-butylbut-2-enyl)-4-hydroxy-2,2,6,6-tetramethylpiperidine

5) 4-stearoyloxy-2,2,6,6-tetramethylpiperidine

6) 1-ethyl-4-salicyloyloxy-2,2,6,6-tetramethylpiperidine

7) 4-methacryloyloxy-1,2,2,6,6-pentamethylpiperidine

8) 1,2,2,6,6-pentamethylpiperidin-4-yl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate

9) di(1-benzyl-2,2,6,6-tetramethylpiperidin-4-yl) maleate

10) di(2,2,6,6-tetramethylpiperidin-4-yl) succinate

11) di(2,2,6,6-tetramethylpiperidin-4-yl) glutarate

12) di(2,2,6,6-tetramethylpiperidin-4-yl) adipate

13) di(2,2,6,6-tetramethylpiperidin-4-yl) sebacate

14) di(1,2,2,6,6-pentamethylpiperidin-4-yl) sebacate

15) di(1,2,3,6-tetramethyl-2,6-diethylpiperidin-4-yl) sebacate

16) di(1-allyl-2,2,6,6-tetramethylpiperidin-4-yl) phthalate

17) 1-hydroxy-4-β-cyanoethoxy-2,2,6,6-tetramethylpiperidine

18) 1-acetyl-2,2,6,6-tetramethylpiperidin-4-yl acetate

19) tri(2,2,6,6-tetramethylpiperidin-4-yl) trimellitate

20) 1-acryloyl-4-benzyloxy-2,2,6,6-tetramethylpiperidine

21) di(2,2,6,6-tetramethylpiperidin-4-yl) diethylmalonate

22) di(1,2,2,6,6-pentamethylpiperidin-4-yl) dibutylmalonate

23) di(1,2,2,6,6-pentamethylpiperidin-4-yl) butyl(3,5-di-tert-butyl-4-hydroxybenzyl)malonate

24) di(1-octyloxy-2,2,6,6-tetramethylpiperidin-4-yl) sebacate

25) di(1-cyclohexyloxy-2,2,6,6-tetramethylpiperidin-4-yl) sebacate

26) hexane-1',6'-bis(4-carbamoyloxy-1-n-butyl-2,2,6,6-tetramethylpiperidine)

27) toluene-2',4'-bis(4-carbamoyloxy-1-n-propyl-2,2,6,6-tetramethylpiperidine)

28) dimethyl-bis(2,2,6,6-tetramethylpiperidin-4-oxy)silane

29) phenyl-tris(2,2,6,6-tetramethylpiperidin-4-oxy)silane

30) tris(1-propyl-2,2,6,6-tetramethylpiperidin-4-yl) phosphite

31) tris(1-propyl-2,2,6,6-tetramethylpiperidin-4-yl) phosphate

32) phenyl[bis(1,2,2,6,6-pentamethylpiperidin-4-yl)] phosphonate

33) 4-hydroxy-1,2,2,6,6-pentamethylpiperidine

34) 4-hydroxy-N-hydroxyethyl-2,2,6,6-tetramethylpiperidine

35) 4-hydroxy-N-(2-hydroxypropyl)-2,2,6,6-tetramethylpiperidine

36) 1-glycidyl-4-hydroxy-2,2,6,6-tetramethylpiperidine

b) Compounds of formula IV ##STR14## wherein n is the number 1 or 2, R and R¹¹ are as defined under a), R¹³ is hydrogen, C₁ -C₁₂ alkyl, C₂ -C₅ hydroxyalkyl, C₅ -C₇ cycloalkyl, C₇ -C₈ aralkyl, C₂ -C₁₈ alkanoyl, C₃ -C₅ alkenoyl, benzoyl or a group of the formula ##STR15## and R¹⁴ when n is 1 is hydrogen, C₁ -C₁₈ alkyl, C₃ -C₈ alkenyl, C₅ -C₇ cycloalkyl, C₁ -C₄ alkyl substituted by a hydroxyl, cyano, alkoxycarbonyl or carbamide group, glycidyl or a group of the formula --CH₂ --CH(OH)--Z or of the formula --CONH--Z, wherein Z is hydrogen, methyl or phenyl, R¹⁴ when n is 2 is C₂ -C₁₂ alkylene, C₆ -C₁₂ arylene, xylylene, a group --CH₂ --CH(OH)--CH₂ -- or a group --CH₂ --CH(OH)--CH₂ --O--D--O--, wherein D is C₂ -C₁₀ alkylene, C₆ -C₁₅ arylene or C₆ -C₁₂ cycloalkylene, or, provided that R¹³ is not alkanoyl, alkenoyl or benzoyl, R¹⁴ can also be a divalent radical of an aliphatic, cycloaliphatic or aromatic dicarboxylic acid or dicarbamic acid or the group --CO--, or R¹³ and R¹⁴ together, when n is 1, can be the divalent radical of an aliphatic, cycloaliphatic or aromatic 1,2- or 1,3-dicarboxylic acid.

Any C₁ -C₁₂ or C₁ -C₁₈ alkyl substituents are as already defined under a).

Any C₅ -C₇ cycloalkyl substituents are especially cyclohexyl.

R¹³ as C₇ -C₈ aralkyl is especially phenylethyl or in particular benzyl.

R¹³ as C₂ -C₅ hydroxyalkyl is especially 2-hydroxyethyl or 2-hydroxypropyl.

R¹³ as C₂ -C₁₈ alkanoyl is, for example, propionyl, butyryl, octanoyl, dodecanoyl, hexadecanoyl or octadecanoyl, but preferably acetyl, and R¹³ as C₃ -C₅ alkenoyl is especially acryloyl.

R¹⁴ as C₂ -C₈ alkenyl is e.g. allyl, methallyl, but-2-enyl, pent-2-enyl, hex-2-enyl or oct-2-enyl.

R¹⁴ as C₁ -C₄ alkyl substituted by a hydroxyl, cyano, alkoxycarbonyl or carbamide group can be e.g. 2-hydroxyethyl, 2-hydroxypropyl, 2-cyanoethyl, methoxycarbonylmethyl, 2-ethoxycarbonylethyl, 2-aminocarbonylpropyl or 2-(dimethylaminocarbonyl)ethyl.

Any C₂ -C₁₂ alkylene substituents are e.g. ethylene, propylene, 2,2-dimethylpropylene, tetramethylene, hexamethylene, octamethylene, decamethylene or dodecamethylene.

Any C₆ -C₁₅ arylene substituents are e.g. o-, m- or p-phenylene, 1,4-naphthylene or 4,4'-diphenylene. D as C₆ -C₁₂ cycloalkylene is especially cyclohexylene.

Preferred compounds of formula IV are those in which n is 1 or 2, R is hydrogen, R¹¹ is hydrogen or methyl, R¹³ is hydrogen, C₁ -C₁₂ alkyl or a group of the formula ##STR16## and R¹⁴ in the case where n=1 is hydrogen or C₁ -C₁₂ alkyl and in the case where n=2 is C₂ -C₈ alkylene.

The following compounds are examples of polyalkylpiperidine compounds of this class:

37) N,N'-bis(2,2,6,6-tetramethylpiperidin-4-yl)hexamethylene-1,6-diamine

38) N,N'-bis(2,2,6,6-tetramethylpiperidin-4-yl)hexamethylene-1,6-diacetamide

39) bis(2,2,6,6-tetramethylpiperidin-4-yl)amine

40) 4-benzoylamino-2,2,6,6-tetramethylpiperidine

41) N,N'-bis(2,2,6,6-tetramethylpiperidin-4-yl)-N,N'-dibutyladipamide

42) N,N'-bis(2,2,6,6-tetramethylpiperidin-4-yl)-N,N'-dicyclohexyl-2-hydroxypropylene-1,3-diamine

43) N,N'-bis(2,2,6,6-tetramethylpiperidin-4-yl)-p-xylylenediamine

44) N,N'-bis(2,2,6,6-tetramethylpiperidin-4-yl)succindiamide

45) di(2,2,6,6-tetramethylpiperidin-4-yl) N-(2,2,6,6-tetramethylpiperidin-4-yl)-β-aminodipropionate

46) the compound of the formula ##STR17## 47) 4-(bis-2-hydroxyethylamino)-1,2,2,6,6-pentamethylpiperidine 48) 4-(3-methyl-4-hydroxy-5-tert-butylbenzamido)-2,2,6,6-tetramethylpiperidine

49) 4-methacrylamido-1,2,2,6,6-pentamethylpiperidine

c) Compounds of formula V ##STR18## wherein n is the number 1 or 2, R and R¹¹ are as defined under a) and R¹⁵ when n is 1 is C₂ -C₈ alkylene, C₂ -C₈ hydroxyalkylene or C₄ -C₂₂ acyloxyalkylene and when n is 2 is the group (--CH₂)₂ C(CH₂ --)₂.

R¹⁵ as C₂ -C₈ alkylene or C₂ -C₈ hydroxyalkylene is, for example, ethylene, 1-methylethylene, propylene, 2-ethylpropylene or 2-ethyl-2-hydroxymethylpropylene.

R¹⁵ as C₄ -C₂₂ acyloxyalkylene is e.g. 2-ethyl-2-acetoxymethylpropylene.

The following compounds are examples of polyalkylpiperidine compounds of this class:

50) 9-aza-8,8,10,10-tetramethyl-1,5-dioxaspiro[5.5]undecane

51) 9-aza-8,8,10,10-tetramethyl-3-ethyl-1,5-dioxaspiro[5.5]undecane

52) 8-aza-2,7,7,8,9,9-hexamethyl-1,4-dioxaspiro[4.5]decane

53) 9-aza-3-hydroxymethyl-3-ethyl-8,8,9,10,10-pentamethyl-1,5-dioxaspiro[5.5]undecane

54) 9-aza-3-ethyl-3-acetoxymethyl-9-acetyl-8,8,10,10-tetramethyl-1,5-dioxaspiro[5.5]undecane

55) 2,2,6,6-tetramethylpiperidine-4-spiro-2'-(1',3'-dioxane)-5'-spiro-5"-(1",3"-dioxane)-2"-spiro-4'"-(2'",2'",6'",6'"-tetramethylpiperidine)

d) Compounds of formulae VIA, VIB and VIC ##STR19## wherein n is the number 1 or 2, R and R¹¹ are as defined under a), R¹⁶ is hydrogen, C₁ -C₁₂ alkyl, allyl, benzyl, glycidyl or C₂ -C₆ alkoxyalkyl, R¹⁷ when n is 1 is hydrogen, C₁ -C₁₂ alkyl, C₃ -C₅ alkenyl, C₇ -C₉ aralkyl, C₅ -C₇ cycloalkyl, C₂ -C₄ hydroxyalkyl, C₂ -C₆ alkoxyalkyl, C₆ -C₁₀ aryl, glycidyl or a group of the formula --(CH₂ )_(p) --COO--Q or of the formula --(CH₂)_(p) --O--CO--Q, wherein p is 1 or 2 and Q is C₁ -C₄ alkyl or phenyl, and R¹⁷ when n is 2 is C₂ -C₁₂ alkylene, C₄ -C₁₂ alkenylene, C₆ -C₁₂ arylene, a group --CH₂ --CH(OH)--CH₂ --O-- D--O--CH₂ --CH(OH)--CH₂ --, wherein D is C₂ -C₁₀ alkylene, C₆ -C₁₅ arylene or C₆ -C₁₂ cycloalkylene, or a group --CH₂ CH(OZ')CH₂ --(OCH₂ --CH(OZ')CH₂)₂ --, wherein Z' is hydrogen, C₁ -C₁₈ alkyl, allyl, benzyl, C₂ -C₁₂ alkanoyl or benzoyl, and T₁ and T₂ independently of the other are hydrogen, C₁ -C₁₈ alkyl or C₆ -C₁₀ aryl or C₇ -C₉ aralkyl which is unsubstituted or substituted by halogen or C₁ -C₄ alkyl, or T₁ and T₂ form a C₅ -C₁₂ cycloalkane ring together with the C atom to which they are bonded.

Any C₁ -C₁₂ alkyl substituents are e.g. methyl, ethyl, n-propyl, n-butyl, sec-butyl, tert-butyl, n-hexyl, n-octyl, 2-ethylhexyl, n-nonyl, n-decyl, n-undecyl or n-dodecyl.

Any C₁ -C₁₈ alkyl substituents can be e.g. the groups listed above and additionally n-tridecyl, n-tetradecyl, n-hexadecyl or n-octadecyl, for example.

Any C₂ -C₆ alkoxyalkyl substituents are e.g. methoxymethyl, ethoxymethyl, propoxymethyl, tert-butoxymethyl, ethoxyethyl, ethoxypropyl, n-butoxyethyl, tert-butoxyethyl, isopropoxyethyl or propoxypropyl.

R¹⁷ as C₃ -C₅ alkenyl is e.g. prop-1-enyl, allyl, methallyl, but-2-enyl or pent-2-enyl.

R¹⁷, T₁ and T₂ as C₇ -C₉ aralkyl are especially phenethyl or in particular benzyl. If T₁ and T₂ form a cycloalkane ring together with the C atom, said ring can be e.g. a cyclopentane, cyclohexane, cyclooctane or cyclododecane ring.

R¹⁷ as C₂ -C₄ hydroxyalkyl is e.g. 2-hydroxyethyl, 2-hydroxypropyl, 2-hydroxybutyl or 4-hydroxybutyl.

R¹⁷, T₁ and T₂ as C₆ -C₁₀ aryl are especially phenyl or α- or β-naphthyl which are unsubstituted or substituted by halogen or C₁ -C₄ alkyl.

R¹⁷ as C₂ -C₁₂ alkylene is e.g. ethylene, propylene, 2,2-dimethylpropylene, tetramethylene, hexamethylene, octamethylene, decamethylene or dodecamethylene.

R¹⁷ as C₄ -C₁₂ alkenylene is especially but-2-enylene, pent-2-enylene or hex-3-enylene.

R¹⁷ as C₆ -C₁₂ arylene is, for example, o-, m- or p-phenylene, 1,4-naphthylene or 4,4'-diphenylene.

Z' as C₂ -C₁₂ alkanoyl is, for example, propionyl, butyryl, octanoyl or dodecanoyl, but preferably acetyl.

D as C₂ -C₁₀ alkylene, C₆ -C₁₅ arylene or C₆ -C₁₂ cycloalkylene is as defined under b).

The following compounds are examples of polyalkylpiperidine compounds of this class:

56) 3-benzyl-1,3,8-triaza-7,7,9,9-tetramethylspiro[4.5]decane-2,4-dione

57) 3-n-octyl-1,3,8-triaza-7,7,9,9-tetramethylspiro[4.5]decane-2,4-dione

58) 3-allyl-1,3,8-triaza-1,7,7,9,9-pentamethylspiro[4.5]decane-2,4-dione

59) 3-glycidyl-1,3,8-triaza-7,7,8,9,9-pentamethylspiro[4.5]decane-2,4-dione

60) 1,3,7,7,8,9,9-heptamethyl-1,3,8-triazaspiro[4.5]decane-2,4-dione

61) 2-isopropyl-7,7,9,9-tetramethyl-1-oxa-3,8-diaza-4-oxospiro[4.5]decane

62) 2,2-dibutyl-7,7,9,9-tetramethyl-1-oxa-3,8-diaza-4-oxospiro[4.5]decane

63) 2,2,4,4-tetramethyl-7-oxa-3,20-diaza-21-oxodispiro[5.1.11.2]heneicosane

64) 2-butyl-7,7,9,9-tetramethyl-1-oxa-4,8-diaza-3-oxospiro[4.5]decane

65) 8-acetyl-3-dodecyl-1,3,8-triaza-7,7,9,9-tetramethylspiro[4.5]decane-2,4-dione

or the compounds of the following formulae: ##STR20##

e) Compounds of formula VII ##STR21## wherein n is the number 1 or 2, R¹⁸ is a group of the formula ##STR22## wherein R and R¹¹ are as defined under a), E is --O-- or --NR²¹ --, A is C₂ -C₆ alkylene or --(CH₂)₃ --O-- and x is the number 0 or 1, R¹⁹ is the same as R¹⁸ or is one of the groups --NR²¹ R²², --OR²³, --NHCH₂ OR²³ and --N(CH₂ OR²³)₂, R²⁰ when n=1 is the same as R¹⁸ or R¹⁹ and when n=2 is a group --E--B--E--, wherein B is C₂ -C₆ alkylene which may be interrupted by --N(R²¹)--, R²¹ is C₁ -C₁₂ alkyl, cyclohexyl, benzyl, C₁ -C₄ hydroxyalkyl or a group of the formula ##STR23## R²² is C₁ -C₁₂ alkyl, cyclohexyl, benzyl or C₁ -C₄ hydroxyalkyl and R²³ is hydrogen, C₁ -C₁₂ alkyl or phenyl, or R²¹ and R²² together are C₄ -C₅ alkylene or C₄ -C₅ oxaalkylene, for example ##STR24## or a group of the formula or R²¹ and R²² are each a group of the formula

Any C₁ -C₁₂ alkyl substituents are, for example, methyl, ethyl, n-propyl, n-butyl, sec-butyl, tert-butyl, n-hexyl, n-octyl, 2-ethylhexyl, n-nonyl, n-decyl, n-undecyl or n-dodecyl.

Any C₁ -C₄ hydroxyalkyl substituents are e.g. 2-hydroxyethyl, 2-hydroxypropyl, 3-hydroxypropyl, 2-hydroxybutyl or 4-hydroxybutyl.

A as C₂ -C₆ alkylene is, for example, ethylene, propylene, 2,2-dimethylpropylene, tetramethylene or hexamethylene.

If R²¹ and R²² together are C₄ -C₅ alkylene or C₄ -C₅ oxaalkylene, this is e.g. tetramethylene, pentamethylene or 3-oxapentamethylene.

The compounds of the following formulae are examples of polyalkylpiperidine compounds of this class: ##STR25##

f) Oligomeric or polymeric compounds whose repeat structural unit contains a 2,2,6,6-tetraalkylpiperidine radical of formula (I), especially polyesters, polyethers, polyamides, polyamines, polyurethanes, polyureas, polyaminotriazines, poly(meth)acrylates, poly(meth)acrylamides and copolymers thereof which contain such radicals.

The compounds of the following formulae are examples of 2,2,6,6-polyalkylpiperidine light stabilizers of this class, m being a number from 2 to about 200: ##STR26##

g) Compounds of formula VIII ##STR27## wherein R and R¹¹ are as defined under a).

Preferred compounds of formula VIII are those in which R is hydrogen or methyl and R¹¹ is hydrogen or methyl.

Examples of such compounds are:

95) 2,2,6,6-tetramethylpiperidin-4-one (triacetonamine)

96) 1,2,2,6,6-pentamethylpiperidin-4-one

97) 1-oxyl-2,2,6,6-tetramethylpiperidin-4-one

98) 2,3,6-trimethyl-2,6-diethylpiperidin-4-one

Polyalkylpiperidines are known compounds and are used as light stabilizers for organic materials. Some of them are commercially available.

Component (C) is a phenolic antioxidant. (C) is preferably a compound of formula I in which A is hydrogen, C₁ -C₈ alkyl, cyclohexyl, phenyl or a group ##STR28## B is C₁ -C₈ alkyl, cyclohexyl or phenyl, X is C₁ -C₈ alkyl or one of the groups --C_(a) H_(2a) --S--R², --C_(b) H_(2b) --COOR³, --CH₂ N(R¹⁰)(R¹¹) and ##STR29## R² is C₁ -C₁₂ alkyl, phenyl or a group --(CH₂)_(c) --COOR⁴, R³ is C₁ -C₁₈ alkyl or a group ##STR30## in which Q is C₂ -C₆ alkylene, --CH₂ CH₂ SCH₂ CH₂ --or --CH₂ CH₂ (OCH₂ CH₂)_(d) --, R⁴ is C₁ -C₁₈ alkyl, R¹⁰ and R¹¹ independently of of the other are C₁ -C₁₂ alkyl or R¹⁰ and R¹¹ together are pentamethylene or 3-oxapentamethylene, a is 1 or 2, b is 1 or 2, c is 1 or 2 and d is 1 to 3, or (C) is a reaction mixture of a phenol of the formula ##STR31## with a phenol of the formula ##STR32## and (para)formaldehyde, in which formulae C, D and E independently of the others are C₁ -C₈ alkyl.

One class which is particularly suitable as component (C) consists of the compounds of formula I in which A and B independently of the other are C₁ -C₄ alkyl, X is a group --C_(a) H_(2a) --S_(q) --R², a is 0 or 1, q is 1 or 2, R² is C₄ -C₁₈ alkyl, phenyl or --CH₂ --CO--OR⁴ and R⁴ is C₁ -C₁₈ alkyl, especially the compounds of formula I in which A and B independently of the other are C₁ -C₄ alkyl, X is --CH₂ --S--R², R² is C₈ -C₁₂ -alkyl or --CH₂ --CO--OR⁴ and R⁴ is C₈ -C₁₈ alkyl. In this class, especially preferred compounds of formula I are those in which A and B are tert-butyl and X is --CH₂ SCH₂ COO(C₈ -C₁₃ alkyl).

Another class which is particularly suitable as component (C) consists of the compounds of formula I in which A and B independently of the other are C₁ -C₄ alkyl, X is a group --C_(b) H_(2b) --CO--OR³, b is 1 or 2 and R³ is one of the groups ##STR33## especially the compounds of formula I in which X is a group --(CH₂)₂ --CO--OR³ and R³ is a group ##STR34## Another class which is particularly suitable as component (C) consists of the methylenebisphenols of the formula ##STR35## wherein A, B and X independently of the others are C₁ -C₁₄ alkyl.

Another class which is particularly suitable as component (C) consists of mixtures of polyphenols obtained by reacting at least one dialkylated phenol of the formula ##STR36## with at least one monoalkylated phenol of the formula ##STR37## and formaldehyde or paraformaldehyde, C, D and E independently of the others being C₁ -C₄ alkyl.

The mixtures formed by this reaction contain predominantly diphenols and triphenols.

Examples of compounds of formula I are: tridecyl 4-(4-hydroxy-3,5-di-tert-butylphenyl)-3thiabutyrate, 3-thiapenta-1,5-diol di[3-(4-hydroxy-3,5-di-tert-butylphenyl)]propionate, di(3-thiapentadecyl) di(4-hydroxy-3,5-di-tert-butylphenyl)malonate, octadecyl 4-(4-hydroxy-3,5-di-tert-butylphenyl)-3-thiabutyrate, 4-(2-thiapropyl)-2,6-di-tert-butylphenol, octadecyl 3-(4-hydroxy-3,5-di-tert-butylphenyl)propionate, 3-thiapentadecyl 3-(4-hydroxy-3,5-di-tert-butylphenyl)propionate, di(4-hydroxy-3,5-di-tert-butylphenyl) sulfide, di(4-hydroxy-3,5-di-tert-butylphenyl) disulfide, 2,4-di(octylthiomethyl)-6-methylphenol, N-octadecyl-3-(4-hydroxy-3,5-di-tert-butylphenyl)propionamide, N,N'-[3-(4-hydroxy-3,5-di-tert-butylphenyl)propionyl]hexamethylenediamine, 4,4'-methylene-bis(2,6-di-tert-butylphenol), 2,2'-methylene-bis(2-tert-butyl-4-methylphenol), 2,4-di(4-hydroxy-3,5-di-tert-butylbenzyl)-6-tert-butylphenol, 4,4'-methylene-bis[2-tert-butyl-4-(4-hydroxy-3,5-di-tert-butylbenzyl)phenol], 4-dimethylaminomethyl-2,6-di-tert-butylphenol, 4-dibutylaminomethyl-2-methyl-6-tert-butylphenol and N-di(4-hydroxy-3,5-di-tert-butylbenzyl)octylamine.

Especially preferred lubricant compositions are those in which (B) is a compound of formula IX or X ##STR38## in which n is 1 or 2, R¹¹ is hydrogen or methyl and Y when n is 1 is --O(C₈ -C₁₅ alkyl) and when n is 2 is a group --NH--(CH₂)₆ --NH-- or --O--CO--(CH₂)_(m) --CO--O-- in which m is 2-8, and (C) is a compound of formula I in which A is hydrogen, C₁ -C₄ alkyl or a group ##STR39## B is C₁ -C₄ alkyl, X is C₁ -C₄ alkyl or one of the groups --CH₂ --S--R², --CH₂ CH₂ COOR³, --CH₂ N(R¹⁰)(R¹¹) and ##STR40## R² is C₁ -C₁₈ alkyl or --(CH₂)₂ --COOR⁴, R³ is C₁ -C₁₈ alkyl or ##STR41## R⁴ is C₁ -C₁₈ alkyl and R¹⁰ and R¹¹ are C₁ -C₈ alkyl, or (C) is a reaction mixture of 2-tert-butylphenol, 2,6-di-tert-butylphenol and (para)formaldehyde.

Components (B) and (C) can be added direct to the base oil or (B) and (C) are first dissolved in a small amount of base oil, with heating if necessary, and the solution is mixed with the remainder of the oil. As a further possibility, a concentrated solution of (B) and (C) in a solvent is mixed with the oil.

The addition of (B) and (C) to the base oil stabilizes the oil against oxidative degradation and reduces the formation of sludge in engine oils.

The lubricant composition can additionally contain other additives, e.g. phosphorus(III) esters, metal passivators, rust inhibitors, agents for improving the viscosity index, pour point depressors, dispersants, surfactants and/or wearing protection additives.

Examples of phosphorus(III) esters are: triphenyl phosphite, decyldiphenyl phosphite, phenyldidecyl phosphite, tris(nonylphenyl) phosphite, trilauryl phosphite, trioctadecyl phosphite, distearylpentaerythritol diphosphite, tris(2,4-di-tert-butylphenyl) phosphite, diisodecylpentaerythritol diphosphite, bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite, tristearylsorbitol triphosphite, tetrakis(2,4-di-tert-butylphenyl)-4,4'-biphenylene diphosphonite and bis(2,6-di-tert-butyl-4-methylphenyl)pentaerythritol diphosphite.

Examples of metal passivators, e.g. for copper, are: triazoles, benzotriazoles and derivatives thereof, tolutriazoles and derivatives thereof, 2-mercaptobenzothiazole, 2-mercaptobenzotriazole, 2,5-dimercaptobenzotriazole, 2,5-dimercaptobenzothiadiazole, 5,5'-methylene-bis-benzotriazole, 4,5,6,7-tetrahydrobenzotriazole, salicylidenepropylenediamine, salicylaminoguanidine and salts thereof.

Examples of rust inhibitors are:

a) Organic acids and their esters, metal salts and anhydrides, e.g.: N-oleoylsarcosine, sorbitan monooleate, lead naphthenate, an alkenylsuccinic anhydride, e.g. dodecenylsuccinic anhydride, alkenylsuccinic acid partial esters and partial amides, 4-nonylphenoxyacetic acid.

b) Nitrogen-containing compounds, e.g.:

I. Primary, secondary or tertiary aliphatic or cycloaliphatic amines and amine salts of organic and inorganic acids, e.g. oil-soluble alkylammonium carboxylates.

II. Heterocyclic compounds, e.g.: substituted imidazolines and oxazolines.

c) Phosphorus-containing compounds, e.g.: amine salts of phosphoric acid partial esters or phosphonic acid partial esters, zinc dialkyldithiophosphates.

d) Sulfur-containing compounds, e.g.: barium dinonylnaphthalenesulfonates, calcium petroleumsulfonates.

Examples of agents for improving the viscosity index are: polyacrylates, polymethacrylates, vinylpyrrolidone/methacrylate copolymers, polyvinylpyrrolidones, polybutenes, olefin copolymers, styrene/acrylate copolymers, polyethers.

Examples of pour point depressors are: polymethacrylate, alkylated naphthalene derivatives.

Examples of dispersants/surfactants are: polybutenylsuccinamides or polybutenylsuccinimides, polybutenylphosphonic acid derivatives, basic magnesium, calcium and barium sulfonates and phenates.

Examples of wearing protection additives are: compounds containing sulfur and/or phosphorus and/or halogen, such as sulfurized vegetable oils, zinc dialkyldithiophosphates, tritolyl phosphate, chlorinated paraffins, alkyl and aryl disulfides and trisulfides, triphenyl phosphorothionates, diethanolaminomethyltolyltriazole, di(2-ethylhexyl)aminomethyltolyltriazole.

The lubricant can also contain solid lubricants such as graphite or molybdenum sulfide.

The following Examples illustrate the invention in greater detail. Percentages are by weight.

EXAMPLE 1

The oxidation behaviour of lubricating oils stabilized according to the invention is tested by the TOST (turbine oxidation stability test) method according to ASTM D-943.

This is performed by adding 60 ml of water to 300 ml of a mineral oil (Mobil STOCK 305) containing 0.05% of a corrosion inhibitor (Reocor® 12) and heating the mixture at 95° C. for 1000 hours, in the presence of iron and copper wire, while oxygen is passed through. The formation of acids is measured by determining the neutralization number TAN (mg KOH/g oil) and the amount of sludge formed (=SLUDGE) is also measured.

The following stabilizers are used: ##STR42## The total amount of stabilizers is 0.25%, based on the oil. The composition of the stabilizer mixture is varied. The results are listed in Table 1.

                  TABLE 1                                                          ______________________________________                                         Proportion            TOST                                                     P-1      H-1          TAN    SLUDGE                                            ______________________________________                                         100%     --           0,19   64 mg                                             95%       5%          0      17 mg                                             90%      10%          0       8 mg                                             75%      25%          0      26 mg                                             ______________________________________                                    

EXAMPLE 2

Testing is carried out as in Example 1, using the following stabilizers: ##STR43## The total concentration is 0.25%, based on the oil.

                  TABLE 2                                                          ______________________________________                                         Proportion           TOST                                                      P-2      H-2         TAN    SLUDGE                                             ______________________________________                                         100%     --          >2     >1000 mg                                           95%       5%         0,26   219 mg                                             90%      10%         0,24   190 mg                                             ______________________________________                                    

EXAMPLE 3

Testing is carried out as in Example 1, using the following stabilizers: ##STR44## The total concentration is 0.25%. The results are listed in Table 3.

                  TABLE 3                                                          ______________________________________                                         Proportion            TOST                                                     P-2      H-3          TAN    SLUDGE                                            ______________________________________                                         100%     --           >2     >1000 mg                                           95%     5%           0,24     180 mg                                          ______________________________________                                    

EXAMPLE 4

Testing is carried out as in Example 1, using the following stabilizers: ##STR45## The total concentration is 0.25%. The results are listed in Table 4.

                  TABLE 4                                                          ______________________________________                                         Proportion            TOST                                                     P-2      H-1          TAN    SLUDGE                                            ______________________________________                                         100%     --           >2     1000 mg                                           95%       5%           0     86 mg                                             85%      15%          0,10   44 mg                                             75%      25%          0,03   75 mg                                             ______________________________________                                    

EXAMPLE 5

Testing is carried out as in Example 1, using the following stabilizers: ##STR46## The total concentration is 0.25%. The results are listed in Table 5.

                  TABLE 5                                                          ______________________________________                                         Proportion            TOST                                                     P-2      H-4          TAN    SLUDGE                                            ______________________________________                                         100%     --           >2     >1000 mg                                          95%       5%          0,18     91 mg                                           90%      10%          0,16     161 mg                                          ______________________________________                                    

EXAMPLE 6

The oxidation resistance of the oils stabilized according to the invention is measured in a differential scanning calorimeter. To do this, a base oil is mixed in a small Al dish with 0.025% of iron(III) acetylacetonate (as oxidation catalyst) and 0.55% of a stabilizer and the mixture is heated isothermally at 160° C. in a calorimeter under 10 bar of oxygen. The time at which the exothermic reaction begins, T_(B) (induction time), and the time at which the exothermic reaction ends, T_(E), are measured: the longer the induction time, the higher the oxidation resistance. The stabilizers used are the phenolic antioxidants P-1 and P-2 and also:

P-3: the reaction product of 160 g of 2,6-di-tert-butylphenol, 40 g of 2-tert-butylphenol, 5.8 g of KOH, 50 ml of ethanol and 24 g of paraformaldehyde at 80° C., containing the following main components: ##STR47##

The results are listed in Table 6.

                  TABLE 6                                                          ______________________________________                                         Stabilizer      T.sub.B (min)                                                                           T.sub.E (min)                                         ______________________________________                                         0,55% P-1        1,47     9,12                                                 0,55% H-5       17,16    22,97                                                 0,45% P-1 +     14,02    27,71                                                 0,10% H-5                                                                      0,55% P-2       16,08    26,07                                                 0,55% H-5       17,16    22,97                                                 0,45% P-2 +     32,27    47,90                                                 0,10% H-5                                                                      0,55% P-3        7,21    14,20                                                 0,55% H-5       17,16    22,97                                                 0,45% P-3 +     50,55    67.97                                                 0,10% H-5                                                                      0,55% P-4        3,00     9,67                                                 0,55% H-5       17,16    22,97                                                 0,45% P-4 +     12,02    20,37                                                 0,10% H-5                                                                      0,55% P-5        4,46    16,44                                                 0,55% H-5       17,16    22,97                                                 0,45% P-5 +     14,10    23,23                                                 0,10% H-5                                                                      ______________________________________                                    

It can be seen from this Table that when using stabilizer mixtures of 0.10% of component A and 0.45% of component B, the oxidation resistance of the oil is higher than would be expected from the data for the individual components.

EXAMPLE 7

The oxidation resistance is tested in a differential scanning calorimeter as in Example 6, except that the measurements are made under 8 bar of air with which 380 ppm of (NO)_(x) have been mixed, rather than under oxygen, and the isothermal temperature is 170° C. Only the beginning of the exotherms is measured.

                  TABLE 7                                                          ______________________________________                                         Stabilizer             T.sub.B (min)                                           ______________________________________                                         0,55% P-2              11,2                                                    0,55% H-5              <2                                                      0,45% P-2 + 0,10% H-5  20,7                                                    0,55% P-6              3,8                                                     0,55% H-5              <2                                                      0,45% P-6 + 0,10% H-5  10,8                                                    ______________________________________                                          P-6                                                                            ##STR48##                                                                 

What is claimed is:
 1. A lubricant composition comprising(A) a mineral or synthetic oil or a mixture of such oils, (B) at least one sterically hindered amine of formula III, IV or VIII ##STR49## wherein R is hydrogen,R¹¹ is hydrogen or methyl, n is 1 or 2, when n is 1, R¹² is C₁ -C₁₈ alkyl, or when n is 2, R¹² is the diacyl radical of an aliphatic dicarboxylic acid having 4 to 12 C atoms, R¹³ is hydrogen, C₁ -C₁₂ alkyl or a group of the formula ##STR50## when n is 1, R¹⁴ is hydrogen or C₁ -C₁₂ alkyl, or when n is 2, R¹⁴ is C₂ -C₈ alkylene; and (C) at least one phenol of formula I ##STR51## in which A and B independently of the other are C₁ -C₄ alkyl,X is a group --C_(b) H_(2b) --CO--OR³, b is 1 or 2, and R³ is one of the groups ##STR52##
 2. A composition according to claim 1, wherein the weight ratio of (B) to (C) is 1:1 to 1:100.
 3. A composition according to claim 1, wherein the weight ratio of (B) to (C) is 1:3 to 1:20.
 4. A composition according to claim 1, wherein the sum of (B) and (C) is 0.05 to 5% by weight of (A).
 5. A composition according to claim 1, wherein (C) is a compound of formula I in which A and B independently of the other are C₁ -C₄ alkyl, X is a group --(CH₂)₂ --CO--OR³ and R³ is a group ##STR53##
 6. A composition according to claim 1 which is an engine oil.
 7. A method for stabilizing a lubricant against oxidative degradation, which comprises incorporating into the lubricant a combination of components (B) and (C) as defined in claim
 1. 8. A method according to claim 7 for reducing the formation of sludge in an engine oil.
 9. A composition according to claim 1 wherein (B) is a compound of formula IX or X ##STR54## in which R¹¹ is hydrogen or methyl,n is 1 or 2, when n is 1, Y is --O(C₈ -C₁₅ alkyl), or when n is 2, Y is a group --NH--(CH₂)₆ --NH-- or --O--CO--(CH₂)_(m) --CO--O-- in which m is 2-8, and (C) is defined as in claim
 24. 10. A composition according to claim 9, wherein (B) is a compound of formula IX in which n is 2 and Y is a group --NH--(CH₂)₆ --NH-- or --O--CO--(CH₂)₈ --CO--O, and (C) is the compound of the formula ##STR55## 